I have been able to observe my noise levels in glorious detail since performing the Konrad i2c modification on my XDR-F1HD. It is becoming very clear why I have had so much difficulty with propagation modes such as meteor scatter and very weak scatter.
Although my location is coastal and I can receive many continental signals virtually all the time, there are periods when nothing seems to get through. It's as if my antenna has been unplugged. Without a signal meter, it has been impossible to know that I had any noise at all since 25dB of noise sounds almost identical to 5 dB of noise, thanks to the white noise heard with FM modulation.
Over the last few weeks I have been able to make three clear observations.
1. Noise levels are constantly variable and timings are random.
2. Noise varies between 14dB - 30dB (No amplification. 4dB = antenna unplugged)
3. There is more than one noise source.
Now I see the picture more clearly I realise that the amounts of noise vary from day to day and it doesn't just depend on the the time of day, thus I can probably rule out thermostatically controlled devices. The intensity of the noise also varies, as does the overall 'sound' of the noise, which can be a smooth 'white noise' or a slightly rough growl. The noise fades in and out too, sometimes slowly over several minutes and sometimes more abruptly in a matter of seconds. It never seems to be instant, as if indicating that somebody has switched on some apparatus, as I had expected it to be.
23dB is more than the amount necessary to get a fully quieting mono signal. Typically I find that a 15 to 18 dB signal can be noise free, unless the noise is present, then a 30dB signal can be noisy. The noise tends to disappear overnight now, returning anytime between 0700 and 0930, according to recent observations. It can be gone at 10:00 or, as is usual, continue throughout the day.
Since the noise levels have become more intermittent here recently, I have been able to hear very weak scatter again. I have also experienced a big improvement in meteor scatter DX.
Sometimes the noise is just as strong in the vertical plane as it is in the horizontal. Sometimes vertical is much quieter. The noise can be stronger at the top of band 2 now, whereas it was always worse at the bottom until recently. Moreover, the direction of the noise now varies between north-east and south-east, though typically it comes from the east. This confirms that there is definitely more than one noise source.
It has always been assumed that the neighbouring property was the source of the noise: 1. Because the directions is correct and 2. because our neighbours use PLT devices and a lot of additional gadgetry due to having a handicapped son, lighting effects, video players, mechanical hoists, etc., much of which is left on constantly. However, our neighbours very recently had to go away for two days. While this doesn't prove or disprove anything, the noise continued in its random fashion throughout the duration of them being away.
Noise is the scourge of modern DXing and there's very little we can do about it, unless we have good neighbours and have the courage to approach them with the purpose of checking their equipment and finding solutions. Having consulted OFCOM recently I was shocked to learn that even relatively simple things like fish tank heaters have been known to propagate high levels of noise high into VHF at a distance of 5 miles!
There was also their story of the radio ham who moved to a remote location, several miles from anybody so he could escape noise. He suddenly discovered one day that he had devastating noise levels and traced them to electricity pylons several miles away.
If you have a clean, quiet band, enjoy it while you can. It may not last.
No comments:
Post a Comment